由熱電子引發銀原子遷移所造成的表面銀奈米顆粒之重組行為

Abstract

在本論文中，我們展示了銀奈米顆粒在不同基板上的重組行為。這種銀奈米顆粒的重組行為使得銀奈米顆粒聚集形成更大的顆粒或者形成雪花形狀的網路圖案。這種現象是由銀奈米顆粒內熱電子產生並遷移進入基板後形成銀離子並溶於吸附的水層擴散引起的。當銀離子和基板內的電子復合，沈積形成一顆新的銀奈米顆粒或連結周圍的銀奈米顆粒。這個重組的過程需要滿足的關鍵因素包括：（1）入射光的光子能量要足夠高使銀奈米顆粒內銀原子的電子發生帶間躍遷或者帶內躍遷以產生熱電子；（2）銀奈米顆粒和基板之間的位能障要足夠低以使熱電子能夠穿越；（3）基板要能導電，使電子可以橫向移動；（4）在銀奈米顆粒和基板表面要存在吸附的水氣。為了測試上述因素，我們分別使用鎵極性和氮極性的氮化鎵基板，矽極性和碳極性的碳化矽基板來觀察不同的銀奈米顆粒的重組現象，也使用兩種不同波長的光源照射以理解在銀奈米顆粒內的電子激發效果。

The behaviors of Ag nanoparticle (NP) reorganization on various templates are demonstrated. The reorganization of Ag NPs may lead to the clustering of Ag NPs to form larger particles or the formation of a networked snowflake-like Ag pattern. Such a phenomenon is caused by the generation of hot electrons in Ag NPs and their migration into the template such that Ag+ ions are formed and dissolved in the adsorbed water for diffusing around. When the Ag+ ions combine with the electrons in the template, it can settle for forming a new Ag NP or connecting neighboring Ag NPs. Therefore, this reorganization process requires the critical factors of (1) the illumination of photons with energy higher than the interband or intraband transition energy of Ag for generating hot electrons in an Ag NP; (2) low enough potential barrier between an Ag NP and the substrate for hot electrons to overcome; (3) conductive substrate for lateral electron transport; and (4) available water vapor around the Ag NP for being adsorbed onto the Ag NP and the template surface. For testing these required factors, we use Ga- and N-face GaN, Si- and C-face SiC templates for observing different Ag NP reorganization behaviors. Two emission wavelengths are used for understanding the effects of electron excitations in Ag NP and template.